It is not a surprise that Thai students score so low on English tests because they don't sense any urgency in learning English.
At the school I work at, they show more enthusiasm for learning Chinese than English. Also, because the Thai "English teachers" don't know how to speak English themselves and the kids learn from this bad example.
It's a shame that they don't consider things like attendance as part of their grade and they also cheat on their assignments and tests with no repercussions. As I was grading my students' finals, which are "supervised", I read the exact same answers on every test in a classroom. These were essay questions and there was the EXACT SAME RESPONSE. But say anything about anything and the school management will not like it.
It's really unfortunate that they don't take school seriously in general. Students are frequently out of class doing "activities". These are usually things like singing and dancing. These activities should be second priority to subjects that prepare them for real life, but it just simply isn't.